The present invention relates to a circuit for exciting a resonator to oscillate at its resonant frequency. The resonator may be an electrical or a mechanical resonator.
For exactly determining the resonant frequency of a resonator, a circuit is commonly required which disturbs the oscillating system as little as possible. Disturbances result in a shift of the resonant frequency, thereby causing errors in measurement.
It is common to excite an oscillating system, such as a string, by pulse sequences of variable frequency and subsequently detect the resonant frequency of the system (string) while it oscillates freely. The frequency of the pulse sequence must be adjusted to a value which is as close as possible to the resonant frequency of the system. To this end, adjustment is made so that the amplitude of the resonant oscillation becomes maximum.
Conventional methods based on this principle are too slow for many applications. They are, in general, suitable only for static systems where the resonant frequency does not vary over substantial periods of time.